In wood frame building construction using two-by-four studs on sixteen inch centers, as is conventionally done, cross bracing at corner posts for added structural strength and resistance to racking is of considerable importance.
Normally, under BOCA basic building code requirements, in buildings that are more than one story in height, and where necessary or desired for added strength in one story buildings, corner posts are made the equivalent of three (3) two-by-four studs with at least a one-by-four continuous brace extending diagonally across the next adjacent studs in each direction from the corner post and which is, preferably, in-set within the studs that it crosses. Or, alternatively, the diagonal bracing may be omitted if wood sheathing in the form of four-by-eight foot panels is applied with approved nailing at the corner sections.
Quite obviously, both the approved form of diagonal bracing and the alternate sheathing or panel method are more expensive and time consumming to accomplish than most builders are willing to put up with. And, moreover, once the skeleton walls are covered, in and out, no one really knows which, if either, method was used and consequently builders can and have been known to ignore these recommended proceedures.
In an effort to simplify corner bracing proceedures, and make it less expensive, attention has been given to providing a metal strip, or "strap", which extends diagonally across the two-by-four studs, out from each corner post, and which is formed to include a flange or leg section received in grooves provided in and aligned across each of the two-by-fours across which the cross bracing member extends.
Such members may be in any of the forms shown and suggested by U.S. Pat. No. 3,875,719 and they may be used for cross bracing, as between floor and roof joists, or wall bracing, as disclosed in the patent.
Of particular concern however, with this type of wind and rack bracing, is its rigidity in compression which depends in large part upon its close fitted or locked engagement in the grooves and to each two-by-four that it extends across. If the fit in the groove is loose then the compressive span is greater and although the channel groove flange may be U-shaped for added structural strength, it can still be buckled under a compressive load in such instances.
To avoid this problem, it is suggested that where the groove fit is loose a nail should be driven down through the U-shaped leg in the receptive groove to spread the side walls for a tighter fit and to hold the leg down in the groove. And, in doing so, about a 16 d nail is required for the cross-sectional breadth and relative length needed. This, in turn, is a sizable nail to be driven into a slot in a two-by-four in a manner that will create side wall pressure and could extend any fault line in the stud.
Also, the lateral flanges in this type of bracing, which offer the best method of tie-down, are not used for tie-down purposes as it is believed they should be.
Accordingly, improvements in this type of wind and rack bracing are considered necessary and are offered herewith.